Video display processor

Abstract

A digital computing system is disclosed having a monolithic microprocessor, a versatile input/output subsystem, a multi-medium memory subsystem, and a video display subsystem with audio generating capability. In the memory subsystem, a balanced mix of dynamic RAM, P-channel MOS ROM and N-channel MOS ROM are included to minimize cost without sacrificing performance. In the video display subsystem, a monolithic video display processor performs all RAM access functions, in addition to composite video generation. The resultant composite video signal, which may include audio and external video information, can be applied directly to a video monitor or RF modulated for use by a television receiver.

What is claimed is: 
     
       1. In a video display system for use with a raster-scanned video display unit, the system including: a random access memory having stored therein a first ordered array of digital code elements which map a set of video color codes into the M columns of N rows of video display elements comprising a first video image; a second ordered array of digital code elements which map said set of video color codes into the S columns of T rows of video display elements comprising a second video image; and a third array containing a column displacement U and a row displacement V for the display of the second video image relative to the first video image, where 1≦S≦M, 1≦T≦N, 1≦U≦M and 1≦V≦N; a video display processor for providing a composite video signal for application to the video display unit, whereby the first video image may be displayed with the second video image superimposed thereon at said column and row displacements, the video display processor comprising:     sequence control means providing a cyclic column count X and a cyclic row count Y indicative of the time sequential position of the raster scan;   memory control means for selectively retrieving from the random access memory, portions of the first, second and third arrays;   overlay control means, cooperating with the memory control means in synchronization with the column and row counts, for providing a first pattern signal comprising the digital code element in the first array which maps the video display element in the column X of the row Y of the first video image when 1≦X≦M and 1≦Y≦N, and for providing a second pattern signal comprising the digital code element in the second array which maps the video display element in the column (X-U+1) of the row (Y-B+1) of the second video image when U≦X<(U+S) and (V≦Y<(V+T);   priority selector means connected to the overlay control means for receiving the first and second pattern signals, selecting the second pattern signal in response to receiving the second pattern signal, selecting the first pattern signal when the second pattern signal is not selected, and providing a video control signal comprised of the video color codes mapped by the digital code elements comprising the selected pattern signal; and   composite video generating means, cooperating with the priority selector means in synchronization with the column and row counts, for generating said composite video signal in accordance with the video color codes of the video control signal.   
     
     
       2. The video display processor of claim 1 wherein the overlay control means comprises: preprocessing means, cooperating with the memory control means 1≦X≦M and 1≦(Y+1)≦N, for retrieving the row displacement V, and for determining if the row count (Y+1) is within a predetermined display range of said row displacement V;   processing means, cooperating with the memory control means when 1≦X≦M and 1≦Y≦N, for retrieving and sequentially providing, as said first pattern signal, the digital code element in the first array which maps the video display element in the column X and row Y of the first video image;   postprocessing means, cooperating with the memory control means when 1≦X≦M and 1≦(Y+1)≦N, for retrieving, in response to the preprocessing means determining that the row count (Y+1) is within the predetermined display range of the row displacement V, the column displacement U and the digital code elements in the second array which map the S video display elements in the (Y-V+1) row of the second video image; and   means, cooperating with the post processing means, for sequentially providing, as the second pattern signal, the digital code element in the second array, retrieved by the postprocessing means, which maps the video display element in the (X-U+1) column of the (Y-V+1) row of the second video image, when U≦X<(U+S) and V≦Y<(V+T).   
     
     
       3. The video display processor of claims 1 or 2 wherein at least a first one of said video color codes corresponds to a video display element having a predetermined color and at least a second one of said video color codes corresponds to a video display element having no predetermined color, and wherein the priority selector means selects the received second pattern signal only when the digital code element comprising the received second pattern signal maps a video color code other than said second video color code. 
     
     
       4. The video display processor of claims 1 or 2 wherein the random access memory has stored therein a plurality of second ordered arrays or digital code elements which map said set of video color codes into the S columns of T rows of video display elements comprising respective second video images, and said third array contains a column displacement U and a row displacement V for the display of each of the second video images relative to the first video image; wherein the overlay control means provides a plurality of second pattern signals, each comprising the digital code element in a respective one of the second arrays which maps the video display element in the column (X-U+1) of the row (Y-V+1) of the respective second video image when U≦X<(U+S) and V≦Y<(V+T); and wherein the priority selector means selects a particular one of the received second pattern signals in accordance with a predetermined prioritized ordering of said second video images. 
     
     
       5. A method for simultaneously display on a raster-scanned video display unit, a first video image comprised of M columns of N rows of video display elements, with a second video image comprised of S columns of T rows of video display elements superimposed thereon beginning at a predetermined column displacement U and a predetermined row displacement V, where 1≦S≦M, 1≦T≦N, 1≦U≦M and 1≦V≦N, the method comprising the steps of: storing a first ordered array of digital code elements which map a set of video color codes into the M columns of N rows of video display elements comprising the first video image;   storing a second ordered array of digital code elements which map said set of video color codes into the S columns of T rows of video display elements comprising the second video image;   storing a third ordered array containing the column displacement U and row displacement V;   providing a cyclic column count X and a cyclic row count Y indicative of the time sequential position of the raster scan;   when 1≦X≦M and 1≦Y≦N, providing a first pattern signal comprising the digital code element in the first array which maps the video display element in the column X of the row Y of the first video image;   when U≦X<(U+S) and V≦Y<(V+T), providing a second pattern signal comprising the digital code element in the second array which maps the video display element in the column (X-U+1) of the row (Y-V+1) of the second video image;   selecting the second pattern signal when the second pattern signal is provided;   selecting the first pattern signal when the second pattern signal is not selected;   providing a video control signal comprised of the video color codes mapped by the digital code elements comprising the selected pattern signal; and   generating said composite video signal in accordance with the video color codes of the video control signal.   
     
     
       6. The method of claim 5 wherein the step of providing the second pattern signal further comprises the steps of; when 1≦X≦M and 1≦(Y+1)≦N, retrieving the row displacement V, and determining if the row count (Y+1) is within a predetermined display range of said row displacement V;   when 1≦X≦M and 1≦Y≦N, retrieving, in response to determining that the row count (Y+1) is within the predetermined display range of the row displacement V, the column displacement U and the digital code elements in the second array which map the S video display elements in the (Y-V+1) row of the second video image; and   when U≦X<(U+S) and V≦Y<(V+T), sequentially providing, as the second pattern signal, the retrieved video display element in the second array which maps the video display element in the (X-U+1) column of the (Y-V+1) row of the second video image.   
     
     
       7. The method of claims 5 or 6 wherein at least a first one of said video color codes corresponds to a video display element having a predetermined color and at least a second one of said video color codes corresponds to a video display element having no predetermined color, and wherein the step of selecting the second pattern comprises selecting the received second pattern signal only when the digital code element comprising the received second pattern signal maps a video color code other than said second video color code. 
     
     
       8. The method of claims 5 or 6 wherein a plurality of the second video images, each comprised of S columns of T rows of video display elements, are superimposed on the first video image beginning at respective predetermined column displacements U and respective predetermined row displacements V; wherein the step of storing the second ordered array comprises storing said plurality of second ordered arrays; wherein the step of storing the third ordered array comprises storing a third ordered array containing each of the respective column displacements U and the respective row displacements V; wherein the step of providing the second pattern signal comprises providing a plurality of second pattern signals, each comprising the digital code element in a respective one of the second arrays which maps the video display element in the column (X-U+1) of the row (Y-V+1) of the respective second video image; and wherein the step of selecting the second pattern signal comprises selecting a particular one of the second pattern signals when at least one of said plurality of a second pattern signals is provided, in accordance with a prioritized ordering of said plurality of second video images.